The present invention contemplates the use of logic-based, morphological operations to isolate image structures requiring size dependent modification, such as features that are susceptible to blooming when reproduced by an output device such as a color xerographic image-on-image, or any other type, of marking engine. The blooming condition, resulting from the need to overexpose the photoreceptor for latter-developed colors that are imaged through an existing colorant, does not lend itself to correction by simple adjustment of xerographic parameters or simple color correction.
Heretofore, a number of patents and publications have disclosed logic-based image processing, the relevant portions of which may be briefly summarized as follows:
Crawford, J. L., and C. D. Elzinga, "Improved Output Quality by Modulating Recording Power," SPSE 41st Annual Conference, May 22-26, 1988, Arlington, Va. Discusses utilizing thickened strokes while performing smoothing, and the use of logical mask processing.
Loce, R. and E. Dougherty, Enhancement and Restoration of Digital Documents, SPIE Press, Bellingham Wash., 1997. Provides much tutorial information oil logic-based image filtering and relevant morphological operations--Section 1.5 teaches the basic relevant operations.
"Method and Apparatus for Digital Image Darkness Control Using Quantized Fractional Pixels," Inventors: R. Bracco, et al., Ser. No. 09/072,122 (May 5, 1997 provisional application, February 1998 actual filing), D/97210P,
Barski, L., and R. Gaborski, "Image Character Enhancement using a Stroke Strengthening Kernel," U.S. Pat. No. 4,791,679, Dec. 13, 1988. Teaches how a character stroke is strengthened by processing video image data with a 16.times.16 kernel, and moving the kernel one pixel at a time through the image. For each pixel position, sections of the kernel, are selectively filled with black pixels in proportion to the number of black pixels in each section, in accordance with a set of predetermined rules.
Crawford, J., and J. Cunningham, "Boldness Control in an Electrophotographic Machine," U.S. Pat. No. 5,128,698, Jul. 7, 1992. Control over the placement of an image edge location on the photoconductor of an electrophotographic machine as providing for a range of discharge levels for edge picture elements (PELS) which vary from greater than, to less than, that level used for fully discharged PELS. Such control is achieved independently of machine parameter control by altering edge PEL illumination intensity in accordance with data representing desired edge PEL intensity as the photoconductor sensitivity changes. A system for measuring and controlling the fully discharged PEL level establishes a measure of photoconductor sensitivity and is used for enabling the selection of current edge PEL intensity. Used control of marking process parameters, as opposed to modifying the digital image.
Mailloux, L., and T. Robson, "Dilation of Images without Resolution Conversion for Printer Characteristics," U.S. Pat. No. 5,483,351, Jan. 9, 1996. An image compensation system which provides dilation or erosion of image features using halfbitting or fullbitting in the rendition of bitmap images, especially on a write-white printer. A region of pixels of an image is isolated which includes two or more correctable pixel locations. A set of state determination rules, based on the formation of pixels in the isolated region, is used to determine a corrected binary pixel state for each of the correctable pixels. Corrections for one correctable pixel may be considered in the state determination rules for adjacent correctable pixels. A single enhanced output pixel is provided for each image input pixel, thereby preserving the original image resolution. Performing enhancements on multiple input pixels. Teaches employment of "halfbits" to thicken strokes by a factional amount while maintaining printer resolution.
Murata, K., "Image Processing Method and Apparatus," U.S. Pat. No. 5,450,208, Sep. 12, 1995. The image processing apparatus for smoothing edges in a reproduced image includes an image data generating circuit for generating image data including a specified pixel and a plurality of pixels surrounding the specified pixel; a sub-pixel data generating circuit for dividing the specified pixel included in the image data into N sub-pixels, for detecting the condition of the specified pixel and the condition of the plurality of pixels surrounding the specified pixel included in the image data by matching the image data with a plurality of predetermined patterns, and for generating sub-pixel data for determining the number and position of sub-pixels to be exposed of the N sub-pixels, based on the condition of the specified pixel and the condition of the plurality of pixels surrounding the specified pixel; and supplying circuit for supplying the sub-pixel data to exposure circuit which makes exposure. The sub-pixel data generating circuit generates sub-pixel data for exposing M sub-pixels of the N subpixels, when the specified pixel is detected to be an exposed pixel which requires no exposure correction, where M is smaller than N. The invention here relates to an image processing method and an image processing apparatus for smoothing jagged edges of characters, etc., and for stably reproducing thin lines and isolated dots, so as to achieve an image reproduction of high quality and to achieve an ideal tone characteristic by correcting the tone characteristic of digital halftone images.